This invention relates to a spindle assembly for a multi-axis machining cell, and specifically, to a spindle assembly having multiple spindles driven in an efficient manner.
Machine tools provided with at least one machining station are typically used for performing drilling, reaming, boring, milling and other machining operations on workpieces.
A machining station of this type essentially includes a machine base upon which is mounted a carrier frame and a machine head. The frame and head may be fitted with a hood that is movable to an open position to allow access to the working area and the various machine tool components located therein.
The carrier frame is slidably movable along horizontal perpendicular paths, designated by axes. The machine head, mounted to a separate carrier, is typically slidably movable perpendicular to the carrier frame along a vertical path (also designated by an axis). The movements of both the carrier frame and the machine head are typically directed by computer-numerically-controlled (CNC) drives.
The machine head of a given machining station includes a motor-driven spindle intended to accommodate and rotatably drive a machine tool for performing a predetermined machining operation on a given workpiece. As discussed above, the tool may be a drill, boring head, milling cutter, or other.
One drawback of these machine tools lies in the fact that it is necessary for the operator to interrupt a given machining operation to load and unload a specific tool within the spindle of the machine head either manually or by using an automatic tool changer. Such a tool change is necessary when both changing the type of tool required for a specific machining operation and when replacing a worn tool of a given type with a new tool.
This tool change procedure often results in a considerable loss of time in the output rate of a given machine and, consequently, during the overall manufacturing cycle. Such losses are contrary to current industrial output requirements with emphasis on high speed machining. Moreover, conventional tool change procedures are not sufficiently reliable for high speed, high volume machining.
To remedy the shortcomings associated with tool change, various tool change mechanisms for automatic transfer (load and unload) of tools between the spindle and storage have been proposed.
Such automated tool change procedure usually includes the following steps: upon signal that a given tool must be exchanged or replaced, the spindle, having the tool inserted therein, must be withdrawn from the workpiece; the rotational speed of the spindle is reduced to zero while the spindle is advanced to the tool storage magazine, where the tools are exchanged; the spindle then withdraws from the magazine, rotationally accelerates to the desired rotational cutting speed, and then advances toward the workpiece for further machining operations.
Such a procedure nonetheless requires an excessive time period for tool change due to the required movements of the spindle between the workpiece and tool storage magazine, as well as due to the deceleration and acceleration of the spindle, as well as clamping and unclamping of a tool within. the spindle. Productivity is necessarily reduced, because during tool exchange, the machine tool is unavailable for operation on the workpiece.
Thus, a need exists for a machine that allows for an exchange of tools during a machining operation while further minimizing the time required for the tool exchange, while also increasing the reliability of tool change and the positional accuracy of the tool setting.
The present invention provides a novel and improved spindle assembly which reduces the foregoing disadvantages associated with the prior art and provides advantages in construction, mode of operation, and use.
To achieve the foregoing, the present invention comprises a single headstock or slide with a plurality of spindles located thereon. Each spindle is operatively connected to a drive motor via a belt and pulley arrangement. Subsets of the plurality of spindles can be driven by the same belt, if desired.
While one of the spindles on the headstock carries out a machining operation on a workpiece, another spindle or spindles, already loaded with tools therein, stand ready for engagement with the workpiece. When the spindle performing a prior operation has completed its task, the spindle carrying a new tool for a subsequent operation can be applied to the workpiece with a minimal delay.
In this manner, the tool exchange time after completion of an operation on the workpiece is limited to that length of time normally required to merely move a spindle from one operating position to another and accelerate across the difference in speed between the two tools. No additional time is required to exchange the tools. Furthermore, no transfer device nor storage magazine is required for tool exchange. Additionally, there is no possibility of introducing contamination at the tool-spindle interface.